(19) Put it in their mouths, that this song may be a witness.--This method of perpetuating the truth was even better adapted to the times and to the condition of the people than the delivery of a written law. It was not possible to multiply copies of the law among them to any great extent; but the rhythmical form of the song would make it easy to be retained in their memories. There is reason to believe that Samuel, the first person who (so far as we know) effected anything of importance towards the establishment of a system of religious education in Israel, employed the same means for the purpose, viz., psalms and spiritual songs. The first companies of prophets were evidently singers and minstrels (see 1Samuel 10:5-6; 1Samuel 19:20-24); hence their remarkable influence over Saul. And if they taught the psalms to the people, as they learnt them under Samuel and David--especially historical psalms, like the 78th, 105th, and 106th--a very efficacious means of spreading the knowledge of God in Israel was in their hands.

Verse 19. - Write ye this song. This refers to the song which follows in next chapter. Moses and Joshua were both to write this song, Moses probably as the author, Joshua as his amanuensis, because both of them were to do their endeavor to keep the people from that apostasy which God had foretold.

31:14-22 Moses and Joshua attended the Divine Majesty at the door of the tabernacle. Moses is told again that he must shortly die; even those who are most ready and willing to die, need to be often reminded of its coming. The Lord tells Moses, that, after his death, the covenant he had taken so much pains to make between Israel and their God, would certainly be broken. Israel would forsake Him; then God would forsake Israel. Justly does he cast those off who so unjustly cast him off. Moses is directed to deliver them a song, which should remain a standing testimony for God, as faithful to them in giving them warning, and against them, as persons false to themselves in not taking the warning. The word of God is a discerner of the thoughts and intents of men's hearts, and meets them by reproofs and correction. Ministers who preach the word, know not the imaginations of men; but God, whose word it is, knows perfectly.Now, therefore, write ye this song for you,.... Which was now dictated by the Lord, and given to Moses and Joshua to write, which is recorded in Deuteronomy 32:1,

and teach it the children of Israel; teach them by it, instructing them in the meaning of it: thus it was usual in ancient times to write things in verses, that they might be the more pleasingly attended to and regarded, and be longer retained in memory; and especially this practice was used with children, and still is:

put it in their mouths; oblige them to get it by heart, or lay it up in their memories, and repeat it frequently, that it may be familiar to them, and not be forgotten by them:

that this song may be a witness for me against the children of Israel; when in times to come they shall call to mind how in this song they were cautioned against such and such sins, and what they were threatened with should befall them on account of them, and how all things have come to pass exactly as foretold in it; which would be a testimony for God of his goodness to them, of his tender care of them, and concern for them, in the previous cautions he gave them; and of his foreknowledge of future events; and a testimony against them for their ingratitude and other sins.